1. Field of Invention
This invention relates to the use of certain agonists of the insulin-like growth factors (IGFs) to treat various disorders.
2. Description of Background and Related Art
The insulin-like growth factors I and II (IGF-I and IGF-II, respectively) mediate multiple effects in vivo, including cell proliferation, cell differentiation, inhibition of cell death, and insulin-like activity (reviewed in Clark and Robinson, Cytokine Growth Factor Rev, 7: 65-80 (1996); Jones and Clemmons, Endocr. Rev., 16: 3-34 (1995)). Most of these mitogenic and metabolic responses are initiated by activation of the IGF-1 receptor, an α2β2-heterotetramer closely related to the insulin receptor (McInnes and Sykes, Biopoly., 43: 339-366 (1997); Ullrich et al., EMBO J., 5: 2503-2512 (1986)). Both proteins are members of the tyrosine kinase receptor superfamily and share common intracellular signaling cascades (Jones and Clemmons, supra). IGF-insulin hybrid receptors have been isolated, but their function is unknown. The IGF-I and insulin receptors bind their specific ligands with nanomolar affinity. IGF-I and insulin can cross-react with their respective non-cognate receptors, albeit at a 100-1000-fold lower affinity (Jones and Clemmons, supra). The crystal structure describing part of the extracellular portion of the IGF-I receptor has recently been reported (Garrett et al., Nature, 394: 395-399 (1998)).
Unlike insulin, the activity and half-life of IGF-I are modulated by six IGF-1 binding proteins (IGFBP's 1-6), and perhaps additionally by a more distantly-related class of proteins (Jones and Clemmons, supra; Baxter et al., Endocrinology, 139: 4036 (1998)). IGFBP's can either inhibit or potentiate IGF activity, depending on whether they are soluble or cell-membrane associated (Bach and Rechler, Diabetes Reviews, 3:38-61 (1995)). The IGFBPs bind IGF-I and IGF-II with varying affinities and specificities (Jones and Clemmons, supra; Bach and Rechler, supra). For example, IGFBP-3 binds IGF-I and IGF-II with a similar affinity, whereas IGFBP-2 and IGFBP-6 bind IGF-II with a much higher affinity than they bind IGF-I (Bach and Rechler, supra; Oh et al., Endocrinology, 132, 1337-1344 (1993)).
The classical IGFBP's have a molecular mass ranging from 22-31 kDa and contain a total of 16-20 cysteines in their conserved amino- and carboxy-terminal domains (Bach and Rechler, supra; Clemmons, Cytokine Growth Factor Rev., 8: 45-62 (1997); Martin and Baxter, Curr. Op. Endocrinol. Diab., 16-21 (1994)). The central domain connecting both cysteine-rich regions is only weakly conserved and contains the cleavage sites for IGFBP-specific proteases (Chemausek et al., J. Biol. Chem., 270: 11377-11382 (1995); Clemmons, supra; Conover, Prog. Growth Factor Res., 6: 301-309 (1995)). Further regulation of the IGFBP's may be achieved by phosphorylation and glycosylation (Bach and Rechler supra; Clemmons, supra). There is no high-resolution structure available for any intact member of the IGFBP family. However, the NMR structures of two N-terminal fragments from IGFBP-5 that retain IGF-binding activity have recently been reported (Kalus et al., EMBO J., 17: 6558-6572 (1998)).
IGF-I is a single-chain 70-amino-acid protein with high homology to proinsulin. Unlike the other members of the insulin superfamily, the C region of the IGF's is not proteolytically removed after translation. The solution NMR structures of IGF-I (Cooke et al., Biochemistry, 30: 5484-5491(1991); Hua et al., J. Mol. Biol. 259: 297-313 (1996)), mini-IGF-I (an engineered variant lacking the C-chain; DeWolf et al., Protein Science, 5: 2193-2202 (1996)), and IGF-II (Terasawa et al., EMBO J. 13: 5590-5597 (1994); Torres et al., J. Mol. Biol. 248: 385-401 (1995)) have been reported. It is generally accepted that distinct epitopes on IGF-I are used to bind receptor and binding proteins. It has been demonstrated in animal models that receptor-inactive IGF mutants are able to displace endogenous IGF-I from binding proteins and hereby generate a net IGF-I effect in vivo (Loddick et al., Proc. Natl. Acad. Sci. USA, 95: 1894-1898 (1998); Lowman et al., Biochemistry, 37: 8870-8878 (1998)). While residues Y24, Y29, Y31, and Y60 are implicated in receptor binding, IGF mutants thereof still bind to IGFBPs (Bayne et al., J. Biol. Chem. 265: 15648-15652 (1990); Bayne et al., J. Biol. Chem. 264: 11004-11008 (1989); Cascieri et al., Biochemistry, 27: 3229-3233 (1988); Lowman et al., supra.
Additionally, a variant designated (1-27,gly4,38-70)-hIGF-1, wherein residues 28-37 of the C region of human IGF-1 are replaced by a four-residue glycine bridge, has been discovered that binds to IGFBP's but not to IGF receptors (Bar et al., Endocrinology, 127: 3243-3245 (1990)).
A multitude of mutagenesis studies have addressed the characterization of the IGFBP-binding epitope on IGF-I (Bagley et al., Biochem. J., 259: 665-671 (1989); Baxter et al., J. Biol. Chem. 267: 60-65 (1992); Bayne et al., J. Biol. Chem. 263: 6233-6239 (1988); Clemmons et al., J. Biol. Chem., 265: 12210-12216 (1990); Clemmons et al., Endocrinology, 131: 890-895 (1992); Oh et al., supra). In summary, the N-terminal residues 3 and 4 and the helical region comprising residues 8-17 were found to be important for binding to the IGFBP's. Additionally, an epitope involving residues 49-51 in binding to IGFBP-1, -2 and -5 has been identified (Clemmons et al., Endocrinology, supra, 1992). Furthermore, a naturally occurring truncated form of IGF-I lacking the first three N-terminal amino acids (called des(1-3)-IGF-I) was demonstrated to bind IGFBP-3 with 25 times lower affinity (Heding et al., J. Biol. Chem. 271: 13948-13952 (1996); U.S. Pat. Nos. 5,077,276; 5,164,370; 5,470,828).
In an attempt to characterize the binding contributions of exposed amino acid residues in the N-terminal helix, several alanine mutants of IGF-I were constructed (Jansson et al., Biochemistry, 36: 4108-4117 (1997)). However, the circular dichroism spectra of these mutant proteins showed structural changes compared to wild-type IGF-I, making it difficult to clearly assign IGFBP-binding contributions to the mutated side chains. A different approach was taken in a very recent study where the IGFBP-1 binding epitope on IGF-I was probed by heteronuclear NMR spectroscopy (Jansson et al., J. Biol. Chem., 273: 24701-24707 (1998)). The authors additionally identified residues R36, R37 and R50 to be functionally involved in binding to IGFBP-1.
Other IGF-I variants have been disclosed. For example, in the patent literature, WO 96/33216 describes a truncated variant having residues 1-69 of authentic IGF-I. EP 742,228 discloses two-chain IGF-I superagonists which are derivatives of the naturally occurring single-chain IGF-I having an abbreviated C domain. The IGF-I analogs are of the formula: BCn, A wherein B is the B domain of IGF-I or a functional analog thereof, C is the C domain of IGF-I or a functional analog thereof, n is the number of amino acids in the C domain and is from about 6 to about 12, and A is the A domain of IGF-I or a functional analog thereof.
Additionally, Cascieri et al., Biochemistry 27: 3229-3233 (1988) discloses four mutants of IGF-I, three of which have reduced affinity to the Type 1 IGF receptor. These mutants are: (Phe23,Phe24,Tyr25)IGF-I (which is equipotent to human IGF-I in its affinity to the Types 1 and 2 IGF and insulin receptors), (Leu24)IGF-I and (Ser24)IGF-I (which have a lower affinity than IGF-I to the human placental Type 1 IGF receptor, the placental insulin receptor, and the Type 1 IGF receptor of rat and mouse cells), and desoctapeptide (Leu24)IGF-I (in which the loss of aromaticity at position 24 is combined with the deletion of the carboxyl-terminal D region of hIGF-I, which has lower affinity than (Leu24)IGF-I for the Type 1 receptor and higher affinity for the insulin receptor). These four mutants have normal affinities for human serum binding proteins.
Bayne et al., J. Biol. Chem., 264: 11004-11008 (1988) discloses three structural analogs of IGF-I: (1-62)IGF-1, which lacks the carboxyl-terminal 8-amino-acid D region of IGF-I; (1-27,Gly4,38-70)IGF-I, in which residues 28-37 of the C region of IGF-I are replaced by a four-residue glycine bridge; and (1-27,Gly4,38-62)IGF-I, with a C region glycine replacement and a D region deletion. Peterkofsky et al., Endocrinology, 128: 1769-1779 (1991) discloses data using the Gly4 mutant of Bayne et al., supra, Vol. 264. U.S. Pat. No. 5,714,460 refers to using IGF-I or a compound that increases the active concentration of IGF-I to treat neural damage.
Cascieri et al., J. Biol. Chem., 264: 2199-2202 (1989) discloses three IGF-I analogs in which specific residues in the A region of IGF-I are replaced with the corresponding residues in the A chain of insulin. The analogs are: (Ile41,Glu45,Gln46,Thr49,Ser50,Ile51,Ser53,Tyr55,Gln56)IGF-I, an A chain mutant in which residue 41 is changed from threonine to isoleucine and residues 42-56 of the A region are replaced; (Thr49,Ser50,Ile51)IGF-I; and (Tyr55,Gln56)IGF-I.
WO 94/04569 discloses a specific binding molecule, other than a natural IGFBP, that is capable of binding to IGF-I and can enhance the biological activity of IGF-I. WO98/45427 published Oct. 15, 1998 and Lowman et al., supra, disclose IGF-I agonists identified by phage display. Also, WO 97/39032 discloses ligand inhibitors of IGFBP's and methods for their use. Further, U.S. Pat. No. 5,891,722 discloses antibodies having binding affinity for free IGFBP-1 and devices and methods for detecting free IGFBP-1 and a rupture in a fetal membrane based on the presence of amniotic fluid in a vaginal secretion, as indicated by the presence of free IGFBP-1 in the vaginal secretion.
Despite all these efforts, the view of the IGFBP-binding epitope on IGF-I has remained diffuse and at low resolution. The previous studies most often involved insertions of homologous insulin regions into IGF-I or protein truncations (e. g. des(1-3)-IGF-I), not differentiating between effects attributed to misfolding and real binding determinants. Combining the results of all these studies is further complicated by the fact that different techniques were used to analyze complex formation of the mutant IGF forms with the IGFBP's, ranging from radiolabeled ligand binding assays to biosensor analysis.
It has been well established that the GH/IGF/IGFBP system is involved in the regulation of anabolic and metabolic homeostasis and that defects in this system may adversely affect growth, physiology, and glycemic control (Jones et al., Endocr. Rev., 16: 3-34 (1995); Davidson, Endocr. Rev., 8: 115-131 (1987); Moses, Curr. Opin. Endo. Diab., 4: 16-25 (1997)). More recent data suggest an expanded role for IGFBPs in the regulation of both plasma levels and bioactivity of GH and IGF-I (Jones et al., supra; Lewitt et al., Endocrinology, 129: 2254-2256 (1991); Rosenfeld et al., “IGF-I treatment of syndromes of growth hormone insensitivity” In: The insulin-like growth factors and their regulatory proteins. Eds Baxter R C, Gluckman P D, Rosenfield R G. Excerpta Medica, Amsterdam, 1994), pp 457-463; Lee et al., Proc. Soc. Exp. Biol. Med., 216: 319-357 (1997); Cox et al., Endocrinology, 135: 1913-1920 (1994); Lewitt et al., Endocrinology, 133: 1797-1802 (1993)). Alterations in IGFBP levels can lead to clinical manifestations of either IGF excess or deficiency and also contribute to GH resistance (Barreca et al., JCEM, 83: 3534-3541 (1998); Shmueli et al., Hepatology, 24: 127-133 (1996); Murphy et al., Prog. Growth Factor Res., 6: 425-432 (1996); Rajkumar et al., Endocrinology, 136: 4029-4034 (1995) Hall et al., Acta Endocrinol. (Copenh), 118: 321-326 (1988); Ross et al., Clin. Endocrinol., 35: 47-54 (1991); Scharf et al., J. Hepatology, 25: 689-699 (1996)).
The two IGFBPs that appear to be most responsible for the regulation of biological activity of both IGFs and GH are IGFBP-1 and IGFBP-3. IGFBP-3 appears to be the IGFBP most responsible for regulating the total levels of IGF-I and IGF-II in plasma. IGFBP-3 is a GH-dependent protein and is reduced in cases of GH-deficiency or resistance (Jones et al., supra; Rosenfield et al., supra; Scharf et al., supra). IGFBP-1 is generally thought to be an inhibitor of IGF activity and is increased in most cases of GH-resistant states such as diabetes, renal failure, congestive heart failure, hepatic failure, poor nutrition, wasting syndromes, and most all catabolic states (Lewitt et al., 1993, supra; Barreca et al., supra; Scharf et al., supra; Bereket et al., Endocrinology, 137: 2238-2245 (1996); Crown and Holly, Clin. Nutrit., 14: 321-328 (1995); Underwood and Backeljauw, J. Int. Med., 234: 571-577 (1993); Thrailkill et al., J. Clin. Endo. Metab. 82(4): 1181-1187 (1997)). Most of these diseases states are characterized by the following biochemical profile: deranged glucose control, inflammation, excess IGFBP-1 levels, low IGFBP-3 levels, low IGF-bioactivity, and excess GH levels (Jones et al., supra; Barreca et al., supra; Shmueli et al., supra; Murphy et al., supra; Rajkumar et al., supra; Hall et al., supra; Ross et al., supra; Bereket et al., supra; Crown and Holly, supra; Bereket et al., Clinical Endocrinology, 45(3):321-326 (1996); Batch et al., J. Clin. Endo. Metab., 73: 964-968 (1991); Powell et al., The Southwest Pediatric Nephrology Study Group, Kidney Int. 51: 1970-1979 (1997)).
Glucocorticoids have been associated with a decrease in protein synthesis and an increase in protein catabolism (Simmons et al., J. Clin. Invest., 73: 412-420 (1984)) and with an increase in the excretion of nitrogen in urine (Sapir et al., Clin. Sci. Mol. Med. 53: 215-220 (1977)). These effects may be partially mediated by a decrease in growth hormone secretion (Trainer et al., J. Endocrinol., 134: 513-517 (1992)) or by direct action of glucocorticoids on the tissue level (Baron et al., Am. J. Physiol., 263: E489-E492 (1992)), resulting in interference with the local production of IGF-I and IGFBPs (McCarthy et al., Endocrinology, 126: 1569-1575 (1990); Lee et al., supra) and antagonism of the action of insulin (Horber et al., Diabetes 40: 141-149 (1991)). Previous studies on rats have demonstrated that the catabolic action of glucocorticoid analogues, such as dexamethasone, can be counteracted by recombinant human IGF-I and its analogues (Tomas et al., Biochem. J. 282: 91-97 (1992)). In addition, insulin has been shown to ameliorate protein catabolism (Woolfson et al., N. Eng. J. Med., 300: 14-17 (1979)).
Combination therapies have also been disclosed. For example, Fuller et al., Biochem Soc Trans, 19: 277S (1991) describes the use of insulin and IGF to stimulate cardiac protein synthesis. Umpleby et al., Europ. J. Clin. Invest. 24: 337-344 (1994) discloses treatment of dogs starved overnight with insulin and IGF to determine the effects on protein metabolism. Additionally, U.S. Pat. No. 5,994,303 discloses the use of a combination of insulin and IGF-I to counteract a decrease in nitrogen balance and protein synthesis.
With respect to renal failure, IGF-I is reported to exert a variety of actions in the kidney (Hammerman and Miller, Am. J. Physiol., 265: F1-F14 (1993)). It has been recognized for decades that the increase in kidney size observed in patients with acromegaly is accompanied by a significant enhancement of glomerular filtration rate (O'Shea and Layish, J. Am. Soc. Nephrol., 3: 157-161 (1992)). U.S. Pat. No. 5,273,961 discloses a method for prophylactic treatment of mammals at risk for acute renal failure. Infusion of the peptide in humans with normal renal function increases glomerular filtration rate and renal plasma flow (Guler et al., Acta Endocrinol., 121: 101-106 (1989); Guler et al., Proc. Natl. Acad. Sci. USA, 86: 2868-2872 (1989); Hirschberg et al., Kidney Int., 43: 387-397 (1993); U.S. Pat. No. 5,106,832). Further, humans with moderately reduced renal function-respond to short-term (four days) IGF-I administration by increasing their rates of glomerular filtration and renal plasma flow. Hence, IGF-I is a potential therapeutic agent in the setting of chronic renal failure (O'Shea et al., Am. J. Physiol., 264: F917-F922 (1993)).
Use of IGF-I or its analogs to treat mammals suffering from kidney disorders such as polycystic kidney disease and related indications, renal dysplasias, and/or renal hypoplasias is described in U.S. Pat. No. 5,985,830. This patent also reports that IGF-I is an effective agent for enhancing glomerular and kidney development in mammals suffering from chronic organ injury.
Additionally, renal function can be enhanced over a period of days by the administration of IGF-I in the setting of end-stage chronic renal failure. This is important, since end-stage chronic renal failure is a condition that can only be treated with dialysis or transplantation and the incidence thereof is rapidly increasing. Diabetics and the elderly tend to have this condition. Approximately sixty percent of patients with end-stage chronic renal failure are on hemodialysis, about ten percent are on peritoneal dialysis, and the remaining about thirty percent receive a transplant. Dialysis therapy is initiated in over 50,000 patients each year in the United States. An additional 25% of patients who have reached end-stage renal failure are denied access to dialysis each year. The cost of caring for these patients on dialysis currently averages over $200 million a month. Furthermore, the patients exhibit an impaired lifestyle on dialysis. Despite the fact that IGF-I can enhance renal function for those experiencing end-stage chronic renal failure, the enhancements of the glomerular filtration rate and renal plasma flow induced by IGF-I short-term do not persist during long-term administration and incidence of side-effects is high (Miller et al., Kidney International, 46: 201-207 (1994)).
The dynamics of IGF-I interaction with sensitive tissues are complex and incompletely understood. Biological activity of circulating IGF-I is regulated by levels of plasma IGFBPs, which both enhance and inhibit IGF-I actions (Cohick and Clemmons, Annu. Rev. Physiol., 55: 131-153 (1993); Kupfer et al., J. Clin. Invest. 91: 391-396 (1993)). In addition, IGFBPs present in tissues regulate the interaction of circulating IGF-I with its receptor. Tissue IGF-I receptor density is altered by changes in levels of circulating IGF-I. In kidney, the numbers of IGF-I receptors are inversely related to levels of circulating IGF-I (Hise et al., Clin. Sci., 83: 233-239 (1992)).
It is known that under some circumstances elevated levels of circulating IGF-I are associated with or directly causative of long-term changes in renal function. For example, the enhancements of insulin and PAH clearances that accompany the elevations of circulating GH and IGF-I in patients with acromegaly are sustained over years of time (Ikkos et al., Acta Endocrinol., 21: 226-236 (1956)). An increase in creatinine clearance occurred within the first 12 days of IGF-I administration to a GH-insensitive Laron dwarf. The increase was progressive over the next 59 days (Walker et al., J. Pediatr., 121: 641-646 (1992)).
GH stimulates the synthesis of IGFBP3 in liver (Hammerman and Miller, supra; Cohick and Clemmons, supra; Kupfer et al., supra). It is the reduction in levels of circulating GH resulting from IGF-I inhibition of pituitary GH release that is thought to result in the fall of circulating IGFBP3 in humans administered IGF-I. Because of their GH insensitivity, IGFBP3 levels are low and are increased by IGF-I in Laron dwarfs (Kanety et al., Acta Endocrinol., 128: 144-149 (1993)). This difference or another in the IGF-I effector system could explain the absence of refractoriness to IGF-I in these individuals.
Walker et al., supra, found that IGF-I increased urinary calcium excretion or urinary volume. Miller et al., supra, did not see such effect. IGF-I also enhances the transport of phosphate across the proximal tubular brush border membrane (Quigley and Baum, J. Clin. Invest., 88: 368-374 (1991)). Patients with long-standing acromegaly showed marked renal hypertrophy and had supranormal glomerular filtration rates, suggesting that the hyperfiltration that accompanies long-standing elevations of circulating GH and IGF-I in humans is not injurious to the kidney (Ikkos et al., supra; Hoogenberg et al., Acta Endocrinol., 129: 151-157 (1993)).
Intermittent administration of IGF-I to treat chronic disorders such as chronic renal failure is disclosed in U.S. Pat. Nos. 5,565,428 and 5,741,776.
Under clinical conditions, circulating IGF-I levels are normal in pre-terminal chronic renal failure (CRF) and slightly decreased in end-stage renal disease (Powell et al., Am. J. Kidney Dis., 10: 287-292 (1987); Blum et al., Pediatr. Nephrol., 5: 539-544 (1991); Tönshoff et al., J. Clin. Endocrinol. Metab., 80: 2684-2691 (1995); Tönshoff et al., Pediatr. Nephrol., 10: 269-274 (1996)). In contrast, IGFBP-1, IGFBP-2, and low molecular weight IGFBP-3 fragments are increased in chronic renal failure serum in relation to the degree of renal dysfunction (Lee et al., Pediatr. Res. 26: 308-315 (1989); Liu et al., J. Clin. Endocrinol. Metab., 70: 620-628 (1990); Powell et al., Pediatr. Res., 33: 136-143 (1993)). The biological action of IGF-I is mediated via the type 1 IGF receptor. Because IGFBPs bind IGFs with affinities similar or higher to those of the type 1 IGF receptor, the excess of unsaturated high-affinity IGFBPs in CRF serum has the ability to inhibit IGF action on target tissues by competing with the type 1 IGF receptor for IGF binding (Tönshoff et al., Prog. Growth Factor Res., 6: 481-491 (1995)). Indeed, increased IGFBP levels in CRF have been identified as inhibitors of IGF bioactivity both in vitro (Blum et al., supra) and in vivo (Tönshoff et al., supra, 1995).
Little is known about the production rates of IGF-I and IGFBPs in CRF. It has been suggested that the constellation of increased IGFBP over normal IGFs indicates a reduced IGF-I secretion rate in CRF, because under normal conditions an increased IGF-binding capacity would be expected to be immediately saturated by IGFs produced in the liver (Blum, Acta Paediatr. Scand. [Suppl] 379: 24-31 (1991)). The previous analysis of plasma IGFBP levels in the setting of clinical CRF had also suggested that an increased IGFBP-2 production rate might contribute to elevated IGFBP levels in CRF plasma (Tönshoff et al., supra, 1995). These two hypotheses were tested by analyzing hepatic IGF-I gene expression and IGFBP-1, -2, -3, and -4 plasma levels in a rat model of experimental uremia, and by analyzing the gene expression of IGFBP-1, -2, and -4 in liver and kidney (Tönshoff et al., Endocrinology, 138: 938-946 (1997)). The authors found that decreased hepatic IGF-I and increased IGFBP-1 and IGFBP-2 gene expression occur in experimental uremia.
For complete reviews of the effect of IGF-I on the kidney, see, e.g., Hammerman and Miller, Am. J. Physiol., 265: F1-F.14 (1993) and Hammerman and Miller, J. Am. Soc. Nephrol. 5: 1-11 (1994).
Treatment of patients having dysregulation of the GH/IGF axis, including renal disorders, with IGF-I may not be successful because of the abnormal distribution of IGFBPs, mainly high IGFBP-1 levels. Therefore, an IGF-I mutant with a reduced affinity for IGFBP-1 without loss of ability to bind to IGFBP-3 could be a unique and effective therapy for the clinical conditions characterized by such dysregulation.